In an Advanced Long Term Evolution (LTE-A) system, in order to improve the throughput of the system and expand the coverage of a network, a Relay Node (RN) is introduced, and as illustrated in FIG. 1, an evolved Node B (eNB) is connected to a Core Network (CN) via a wired interface, and an RN is connected to the eNB via a wireless interface; a User Equipment (UE) is connected to the RN or the eNB via a wireless interface. A link between the RN and the eNB is referred to as a backhaul link, and a link between the RN and the UE is referred to as an access link.
A certain time delay is required for transmission of a signal sent from the eNB to the RN over the backhaul link in both a Time Division Duplex (TDD) system and a Frequency Division Duplex (FDD) system, and the time delay is related directly to the distance between the eNB and the RN. From the perspective of the RN side, a downlink signal received over the backhaul link is subjected to this delay, as illustrated in FIG. 2.
As can be seen from FIG. 2, synchronized initialization and synchronized tracking with the downlink of the eNB is performed in the downlink of the relay backhaul link through a downlink signal (e.g., a primary synchronization signal, a secondary synchronization signal and a pilot signal) transmitted from the eNB.
FIG. 3 illustrates a downlink transmission time of an RN access link synchronized with a downlink receipt time of an RN backhaul link. Downlink transmission of the eNB may not be synchronized with downlink transmission of the RN if the RN is considered as a separate eNB.
The inventors have discovered the following technical problem in the prior art during implementing the invention:
Downlink transmission of the eNB may not be synchronized with downlink transmission of the RN and also a specific solution to synchronizing downlink transmission of the eNB with downlink transmission of the RN has been absent at present.